In a communications system, a receiver is used to receive a signal, and determine, through computation, a sent sequence that is on a sending terminal and corresponds to a received sequence. In algorithms for determining a sent sequence, maximum likelihood sequence estimation (MLSE) can compensate for linear and nonlinear losses in the system, reduce a bit error rate, and achieve a better effect.
A basic principle of MLSE is to find, among all possible sent sequences, a sequence that is most consistent with a received sequence, and set this possible sent sequence as a detected sent sequence. Generally, a Viterbi algorithm (VA) is used to make complexity no longer related to a quantity of elements in a sequence, and thereby reduce complexity of MLSE. In this case, the two algorithms are jointly referred to as MLSE-VA. A consideration of the VA is to remove a survivor path that cannot become a maximum likelihood selection object on a lattice diagram.
However, in high-order quadrature amplitude modulation (QAM), as a system order increases, a quantity of operations in the MLSE-VA algorithm increases exponentially. Therefore, a method for detecting a sent sequence still includes a large quantity of operations and has low efficiency.